Oxidation Polymerization And Optical Properties Of Polymer Light-Emitting Materials

Polymer light-emitting diodes (PLED) have recently attracted a great deal of attention due to their physical properties and their potential applications in light emitting device and flat panel displays. To develop a full-color display, the design and synthesis of light-emitting materials are particularly important. The 9,9'-spirobifluorene-based polymers are one of the most promising candidate for use in blue PLED because of the special spiro-structure. Polyspirobifluorene is a classic blue-emission polymer and a good electron-transporting material. Previous studies have shown that incorporating a 9,9'-spirobifluorene linkage into the structure of polymeric materials, leads to a reduction in crystallization tendency and an increase in glass transition temperature. Also most of the desired electronic and optical properties of the corresponding nonspiro molecules are preserved. However, poor processability due to rigid ring structure is still a problem for preparation and application for devices.In this paper, various wide bandgap conjugated polymers such as polycabazole and polytriphenylamine are introduced into 9,9'-spirobifluorene unit, via oxidation polymerization, and two series of the polymers are poly(9,9'-spirobifluorene-co-cabazole), poly(9,9'-spirobifluorene-co-triphenylamine). FTIR spectra is used to characterize the polymer structures. The PL spectrum of polymers indicates that there is a wide PL maximum around 410 nm, and the emission color of the polymers is blue. The shoulder peak of Poly(SPF-CAS) in the PL spctrum disappears when the feed ration of SPF/CAS is 1:3.Besides we design and synthesize spirobifluorene-based polymers having alkoxy hydrocarbon chains. As well known, the performance of solubility and electron transport can be further improved when copolymerized with alkoxy side chain moiety by the chemical modifications. The alkoxy side chain group plays an important role in improving the solubility of the corresponding copolymers. So a series of polymers are synthesized via oxidation polymerization. UV-vis absorption spectra of polymers show that the absportion peaks are a single sharp in diluted solutions. The polymers films spin-coated from chloroform(CHCl3) solution onto a quartz plate are shown that the position of UV-vis absportion peaks red-shifts 6-10 nm compared with the polymers in solutions. The PL spectrum indicates because of increasing the length ofπ-π*conjugate chain, the spectrum of the emission and the excitation overlap which means it is easy for the efficient energy to transfer. With quinine sulfate solution as a reference, three of polymers fluorescence quantum yields are measured to be 0.7. Thermal analysis results show that the high thermal stabilities of these polymers with the rigid and bulk spiro-segement unit in the polymer main chain. Cyclic voltammetry (CV) tests indicate that the highest occupied molecular orbital (HOMO) energy levels of the copolymers are located between -5.85 and -5.69 eV. The solubility test shows that good solubility can be attributed to the presence of the long alkoxy chain in the polymers. It is noteworthy that the polymers present best solubility when the feed of ration of 9,9'-spirobifluorene and alkoxy-benzen is 1:1.